Dr. Oz says many factors contribute to medical mistakes. First, he says doctors shouldn't be using pens and pencils—19th-century tools—in a 21st-century world. "Computerized order entry and, more importantly, these bar coding systems that Dennis is talking about have dramatically changed the way practice is conducted in hospitals," Dr. Oz says.

Over the past five years, Dr. Oz says hospitals that have adopted the "grocery store" system have eliminated dosage errors. "We're not talking about a small little jump here," he says. "We're talking about a dramatic shift."

Mistakes also happen because hospitals are busy places. "There's a lot of things happening at once. People get tired," Dr. Oz says. "They get interrupted all the time."